EP2883688B1 - Composite annular casing of a turbomachine compressor and method for its manufacture - Google Patents

Description

Technical area

The invention relates to a composite outer annular casing of an axial turbomachine. More specifically, the invention relates to a composite annular casing of an axial turbomachine having a circular wall, a radial annular flange and a sharp edge at their junction; the composite comprising a fiber preform. The invention also relates to an axial turbomachine comprising a composite annular casing. The invention also relates to a method of manufacturing a composite annular casing for an axial turbomachine.

Prior art

In order to lighten a turbomachine, some of its elements conventionally produced in metal can be made of a composite material. Structuring elements such as supports, housings can be produced in a composite material. In particular, an external compressor casing, in particular low pressure, can be produced in a composite material.

Such a housing generally has a cylindrical portion which supports annular rows of blades, and annular fixing flanges which extend radially. The flanges allow the compressor casing to be mounted on an intermediate fan casing, and the attachment of an annular separating nozzle. The internal surface of the casing makes it possible to guide the annular flow along the compressor, and for this purpose must have a smooth surface; without jumps. This constraint requires making sharp edges at the level of the fixing flanges.

A composite compressor outer casing can be made from a preform densified by a die. The preform may be formed from a stack of fibrous sheets stacked on top of each other, the sheets extending both over the cylindrical portion and over the securing flanges. Once shaped, the preform is placed in a mold injection having ridges to reproduce the desired shape of the housing. However, the stacked preform forms a rounding at the level of the edge of the mold and leaves an empty space there. During injection, the space is filled with resin without being reinforced by fibers. Therefore, the composite housing exhibits a weakness in this location.

It is known from the document GB 2486231 A a tool for shaping a preform of a composite turbomachine casing, the casing having radial annular flanges at its upstream and downstream ends. The preform comprises a stack of plies which are shaped in the forming tool, so as to generate the annular flanges. In order to limit the appearance of a rounding of the preform under the flanges during its shaping, the tool comprises movable blocks shaping the flanges; the preform being placed beforehand in a membrane in which a suction is created. This teaching makes it possible to approach a desired geometry, however it requires expensive tools. Moreover, the rounding occupied by the preform depends on the thickness of the lower ply. The rounding can be deformed due to the aspiration.

The document EP 1 900 502 A1 discloses an annular composite component of a turbomachine. The component has an annular body and annular flanges at the ends, and sharp annular ridges within the flanges. The composite component comprises several fibrous reinforcements, one of which is frayed at the edges so as to distribute the fibers therein in the junctions between the flanges and the annular body. The teaching of this document makes it possible to distribute fibers in the junctions, but causes heterogeneity in the density of fibers. This heterogeneity reduces the mechanical resistance of the composite component, and in particular in the face of a bending force applied to a flange. The document EP2077183 A1 discloses a method of making a composite casing. The casing has an annular wall and a radial flange, the junction of which has a sharp edge. The latter is reinforced by a first fibrous structure in contact with the main fibrous structure. This configuration preserves the main structure during machining. However, the very resistance of the edge remains limited.

Summary of the invention Technical problem

The object of the invention is to solve at least one of the problems posed by the prior art. Another objective of the invention is to reinforce an annular junction between a fixing flange and a circular wall of a composite outer annular casing of a turbomachine. The object of the invention is also to reinforce as closely as possible a sharp edge under an annular flange of the composite outer annular casing of the turbomachine. Technical solution

The invention relates to a composite annular casing of a turbomachine according to Claim 1, in particular of a low-pressure compressor.

According to an advantageous embodiment of the invention, the core of the auxiliary reinforcement comprises a strand preferably braided or woven, optionally in a three-dimensional manner.

According to an advantageous embodiment of the invention, the cross section of the core of the auxiliary reinforcement has a profile generally in a triangle, optionally in a right triangle, the right angle of which is disposed at the level of the sharp edge.

According to an advantageous embodiment of the invention, the main reinforcement and the auxiliary reinforcement are essentially in contact over the entire radial thickness of the wall and / or over the entire axial thickness of the fixing flange.

According to the invention, the core of the auxiliary reinforcement comprises fibers which extend radially from the edge to the main reinforcement, preferably the core of the auxiliary reinforcement has a homogeneous fiber density perpendicular to its elongation.

According to an advantageous embodiment of the invention, the fixing flange is an annular fixing flange and / or an axial fixing flange, preferably the annular casing is an annular half-casing extending over a semicircle which comprises flanges axial arranged laterally on the cylindrical portion and opposing annular flanges disposed at the axial ends of the cylindrical portion.

According to an advantageous embodiment of the invention, the fibers of the core of the auxiliary reinforcement extend mainly parallel to the edge, preferably each portion of fibers of the auxiliary reinforcement (56) is inclined relative to the edge at a lower angle. at 40 °, more preferably less than 20 °.

According to the invention, the core of the auxiliary reinforcement comprises fibers of the same type as the main reinforcement, preferably the fibers of the main reinforcement and of the core of the auxiliary reinforcement are of the same length and / or of the same diameter.

According to an advantageous embodiment of the invention, the fibers of the main reinforcement and of the core of the auxiliary reinforcement are imbricated at the interface between the main reinforcement and the auxiliary reinforcement, preferably the fibers of the reinforcements are arranged in bundles of fibers which are interwoven with the through the interface.

According to an advantageous embodiment of the invention, the main reinforcement and the core of the auxiliary reinforcement each have a homogeneous fiber density, preferably the ratio of the fiber densities of the reinforcements is between 0.5 and 1.50; preferably between 0.80 and 1.20; more preferably between 0.95 and 1.05.

According to an advantageous embodiment of the invention, the section of the core is symmetrical.

According to an advantageous embodiment of the invention, each fiber portion of the core is inclined relative to the axis of elongation of the casing by an angle of between 50 ° and 130 °, preferably between 60 ° and 120 °, more preferably between 75 ° and 105 °.

According to an advantageous embodiment of the invention, the core conforms to the main reinforcement over the majority, preferably over the entire radial height of the core.

According to an advantageous embodiment of the invention, the casing has continuity of material between the fixing flange and the wall.

According to an advantageous embodiment of the invention, the envelope of the core delimits a space which occupies at least 15%, preferably at least 25%, more preferably at least 35% of the junction between the flange and the wall of the annular casing.

According to an advantageous embodiment of the invention, the matrix and the core form the sharp edge.

According to an advantageous embodiment of the invention, the casing comprises a flange extending perpendicularly to the wall.

The invention also relates to a turbomachine according to claim 11.

According to an advantageous embodiment of the invention, the turbomachine comprises an intermediate fan casing, a low pressure compressor with annular rows of stator vanes and a separating nozzle, the annular casing comprising an annular fixing flange at each axial end, including an upstream flange and a downstream flange, the annular casing having a reduction in radius downstream, preferably the annular casing is an external main structure of the compressor on which the rows of blades are fixed, the separating nozzle via the flange upstream, the intermediate fan casing via the downstream flange, the annular casing further comprising an alternation of annular layers of abradable material and annular blade fixing surfaces, the annular casing is formed of half-shells separated by a plane s 'extending axially.

The invention also relates to a method, according to claim 13, for manufacturing a composite annular turbomachine casing.

According to an advantageous embodiment of the invention, before step (b) of placing a main reinforcement, said reinforcement is produced with a rounding intended to come into contact with a contact surface of the auxiliary reinforcement, preferably at after step (b) the rounding of the main reinforcement flattens out and the contact surface of the auxiliary reinforcement is curved.

According to an advantageous embodiment of the invention, during step (c) closing of the injection mold, the main reinforcement is compacted and / or the main reinforcement and the core compact each other.

According to an advantageous embodiment of the invention, when the mold is closed, the core conforms over its entire radial height to the surface of the mold which forms the flange.

Benefits provided

The invention makes it possible to reinforce a sharp edge of a turbomachine casing. The fiber density can be homogeneous, which optimizes the mechanical strength. The distribution of the fibers on either side of the edge can be symmetrical, which improves the mechanical properties. The process makes it possible to produce a sharp edge with precise ribs and a sharp edge, without requiring additional machining.

Brief description of the drawings

• The figure 1 represents an axial turbomachine according to the invention.
• The figure 2 is a diagram of a turbomachine compressor according to the invention.
• The figure 3 is a diagram representing the method of manufacturing a housing according to the invention.
• The figure 4 shows schematically a main fiber reinforcement of the housing according to the invention.
• The figure 5 illustrates a section of the main fiber reinforcement of the housing according to the invention along the line 5-5 drawn on the figure 4 .
• The figure 6 shows schematically an auxiliary fibrous reinforcement of the casing according to the invention.
• The figure 7 represents the step of the method of placing the auxiliary fibrous reinforcement in the mold according to the invention.
• The figure 8 represents the stage of the process for placing the main fibrous reinforcement in the mold according to the invention.
• The figure 9 represents an intermediate state of the process where the reinforcements are placed in the mold according to the invention.
• The figure 10 represents the stage of the method of closing the mold according to the invention.
• The figure 11 represents the step of the method of injecting a resin into the mold according to the invention.
• The figure 12 represents the stage of the process for demolding the casing according to the invention.

Description of the embodiments

In the description which follows, the terms internal or internal and external or external refer to a positioning with respect to the axis of rotation of an axial turbomachine.

In the description which follows, the terms internal or internal and external or external refer to a positioning with respect to the axis of rotation of an axial turbomachine.

The figure 1 shows in a simplified manner an axial turbomachine. In this specific case, it is a double-flow turbojet. The turbojet 2 comprises a first level of compression, called low-pressure compressor 4, a second level of compression, called high-pressure compressor 6, a combustion chamber 8 and one or more levels of turbines 10. In operation, the mechanical power of the turbine 10 transmitted via the central shaft to the rotor 12 sets in motion the two compressors 4 and 6. Reduction means can increase the speed of rotation transmitted to the compressors. Or, the different turbine stages can each be connected to the compressor stages via concentric shafts. The latter have several rows of rotor blades associated with rows of stator vanes. The rotation of the rotor around its axis of rotation 14 thus makes it possible to generate an air flow and to gradually compress the latter up to the entrance of the combustion chamber 8.

An inlet fan commonly referred to as fan 16 is coupled to rotor 12 and generates an air flow which is divided into a primary flow 18 passing through the various aforementioned levels of the turbomachine, and a secondary flow 20 passing through an annular duct (partially shown) along the machine to then join the primary flow at the turbine outlet. The primary 18 and secondary 20 flows are annular flows, they are channeled by the casing of the turbomachine.

The figure 2 is a sectional view of a compressor of a turbomachine axial 2 such as that of the figure 1 . The compressor can be a low-pressure compressor 4. It can be seen part of the fan 16 and the spout 22 for separating the primary flow 18 and the secondary flow 20. The rotor 12 comprises several rows of rotor blades 24, in l occurrence three.

The compressor comprises several rectifiers, in this case four, which each contain a row of stator vanes 26. The rectifiers are each associated with a row of rotor vanes to straighten the air flow, so as to convert the speed of the rotor. pressure flow.

The compressor comprises at least one casing 28. The casing 28 may have a generally annular shape with a profile of revolution about the axis of rotation 14 of the turbomachine. It can be an external casing and can be made of composite materials. It can be essentially flat. The annular casing 28 may comprise fixing flanges 30, for example annular fixing flanges for fixing the separation nozzle 22 and / or for fixing to an intermediate fan casing 32 of the turbomachine. The annular flanges 30 may include fixing holes (not shown) to allow fixing by bolts, or by lockbolts.

The composite annular casing 28 may include a generally circular or arcuate wall 34, the edges of which may be delimited by the flanges 30. The wall 34 may have an ogive shape, with a variation in radius along the length of the wall. axis 14. This evolution of the radius can be reversed. The wall 34 has an inner surface with a double curvature, one of the curvatures being along an axial plane, the other curvature being along a radial plane. It is understood that the radial plane is perpendicular to the axis 14, the axial plane extends axially and radially.

The wall 34 may have annular blade fixing surfaces and / or series of fixing holes (not shown) arranged in annular rows for fixing the stator vanes 26. The fixing holes can be provided with inserts ( not shown) to reinforce the composite material of the annular casing 28. The inserts can be integrated into the thickness of the wall 34 or of the flanges 30.

The annular casing 28 can also be a support for annular layers of abradable material 36 which are disposed against the wall 34 and which are intended to ensure a seal with the outer ends of the rotor blades 24. The annular surfaces of the blade attachments and the abradable layers 36 can form an alternation. The annular casing 28 comprises a composite material, for example with an organic matrix and carbon fibers. The annular casing 28 includes a main fiber reinforcement and an auxiliary fiber reinforcement.

The figure 3 represents a diagram of the manufacturing process of the composite annular casing.

1. (a) une première étape de mise en place du renfort fibreux auxiliaire (107) ;
2. (b) une deuxième étape de mise en place du renfort fibreux principal (108) ;
3. (c) une troisième étape de fermeture du moule d'injection (110) ;
4. (d) une quatrième étape d'injection et de polymérisation (111) ;
5. (e) une cinquième étape de démoulage et éventuellement d'usinage (112).

The method comprises the succession, optionally in this order, of the following steps:

1. (a) a first step of placing the auxiliary fibrous reinforcement (107);
2. (b) a second step of placing the main fibrous reinforcement (108);
3. (c) a third step of closing the injection mold (110);
4. (d) a fourth injection and polymerization step (111);
5. (e) a fifth demoulding and optionally machining step (112).

The first step 107 comprises a step of providing or producing an auxiliary fibrous reinforcement. It can be carried out several times so as to have an auxiliary reinforcement in each re-entrant edge or corner of the mold. Optionally, it may consist in placing an auxiliary reinforcement forming a loop along the contour of the annular portion. For example, the auxiliary reinforcement can run alongside two axial flanges and two annular flanges.

The second step 108 comprises a step of providing or producing a main fibrous reinforcement. According to an alternative of the invention, the reinforcements can be made before the first step of the process. The main reinforcement can be made directly from the mold by stacking of fibrous folds or by stacking of fibrous folds on a external preforming support. Each ply can be woven so as to present in advance the shape that it should occupy when it is placed in the mold. The folds can be held together by sewing them, gluing them punctually.

The steps presented above as well as the elements employed are detailed in more detail in the following paragraphs.

The figure 4 shows a section of the main fiber reinforcement 38 of the housing. The present teaching can be applied to any casing of the turbomachine.

The main fibrous reinforcement 38 can have a symmetry of revolution with a profile of revolution with respect to the axis 14. It can be flat. It comprises a fiber preform 40, which has been formed so as to roughen the shape of the composite annular casing. The preform 40 may have a circular wall 42, or in an arc of a circle, intended to reinforce the wall of the annular casing, and at least one, preferably two annular fixing flanges 44 which extend radially and which are intended to reinforce the flanges. annulars of the annular housing.

The preform 40 comprises a stack of fibrous plies 46, which may extend over the partition 42, and over at least one or more fixing flanges 44. Each ply 46 may extend over an axial portion of the partition 42. Thus, , the number of folds 46 can vary axially. The number of folds may increase downstream. At least one ply 46 can be added to reinforce the junction between the partition 42 and one of the flanges 44. The preform 40 can comprise a layer with a fibrous mat which has, depending on its thickness, several levels of fibers, for example at least two. preferably at least four, more preferably at least ten levels of fibers.

The plies 46 can comprise carbon fibers, and / or graphite fibers, and / or glass fibers. Advantageously, the preform can include several types of folds. For example, the preform may include a core layer with carbon fiber plies, and at the minus a fold with glass fibers on the surface, possibly to prevent galvanic corrosion.

The plies 46 are woven plies, the latter may comprise fibers and / or bundles of fibers woven in two directions, for example perpendicular. Each bundle of fibers may have several fibers depending on its section. Optionally, a fibrous ply has three directions of weaving.

The preform 40 can include at least five plies 46, preferably at least twelve plies 46, more preferably at least twenty plies 46 depending on its thickness. The folds 46 may form a sharp angle at the junction between the partition 42 on the radially outer side of the preform 40. Inside, under each annular flange 44, the preform may form an annular rounding 50 or elbow which results from the winding of the folds on the sharp angle.

The figure 5 shows a section of the main fiber reinforcement 38 of the composite annular casing along the line 5-5 drawn on the figure 4-4 .

The annular casing can describe a circle. It may be an annular half-casing which describes a semicircle, or an annular segment of an annular casing which describes a fraction of a circle; like a quarter, a sixth, or an eighth of a circle.

The annular casing can be divided along one or more planes which extend along the axis of rotation 14. To join the half-casings or the casing segments, these are provided with axial fixing flanges intended to be fixed to the casings. to each other, and can form a smooth circle, without a step. Therefore, the partition, and the wall can be half-tubes, and extend over a semicircle, or be fractions of a circle. The assembly of half-casings or casing fractions makes it possible to describe a closed circle.

The main reinforcement 38 of the annular casing can also describe a semi-circle so as to reinforce the semi-casing. The main reinforcement can have axial fixing flanges 52, which extend radially and which can follow a sinusoid. The main reinforcement 38 can be produced by a successive stack of fibrous folds 46, axial roundings 54 may appear at the edge of the wall, at the axial junction with the axial flanges, all along the axial flanges 52.

The figure 6 shows a section of the auxiliary fiber reinforcement 56 of the housing.

The auxiliary fibrous reinforcement 56 comprises a core 58. The core 58 may be a strand of fibers 60, optionally woven or braided three-dimensionally. Its fibers 60 can describe spirals along the ridge. The fibers 60 and / or the bundles of fibers of the core 58 are of the same nature as the fibers of the preform. By the same nature we can understand the same material, and / or the same length and / or the same diameter.

The auxiliary reinforcement 56 may comprise portions extending radially or axially the core 58. The core 58 may have an elongation and a cross section along a plane perpendicular to its elongation. Its cross section can generally be a polygon, such as a triangule, possibly a rectangle and / or isosceles. The maximum height H of the triangle of the profile of the core 58 is substantially equal to the thickness of one of the flanges and / or the thickness of the wall of the first preform. Said height is measured radially when the auxiliary reinforcement 56 is placed in the mold, it can be between 60% and 140%, preferably between 90% and 110% of the thickness of one of the flanges and / or of the thickness. of the wall of the first preform. The core 58 can have a substantially constant fiber density.

The fibers 60 of the core 58 can be mainly oriented parallel to the elongation of the auxiliary reinforcement 58. Each of their portions forms an angle of less than 45 ° with respect to the elongation of the auxiliary reinforcement, preferably less than 20 °.

The figure 7 represents a first step of the manufacturing process of the composite annular casing according to the invention. A mold portion is shown in section on a plane passing through an axis which corresponds to the axis 14.

The method employs an injection mold with a first mold 62. The first step includes placing the auxiliary reinforcement 56 inside the first mold 62, with its core against a surface of. molding 64. The mold 62 can be a mold making it possible to produce an annular casing, a segment of the annular casing or a half-shell. It can have molding surfaces generated by a profile of revolution. The mold may have a generally tubular annular molding surface 66 which is the conjugate of the interior surface of the annular housing. Although the tubular molding surface shown here is straight, it is obvious that in practice it can have any curved shape making it possible to produce an axial flange or an annular flange.

The mold 62 may also have a radially extending molding surface 68, which is the conjugate of an attachment surface of one of the flanges. The tubular surface 66 and the radial surface 68 form a corner 70 or re-entrant angle 70 at their junction. In order to fill this corner 70, the auxiliary reinforcement 56 is applied to it.

Although only one auxiliary reinforcement 56 is shown, it is conceivable to apply others, for example at an opposite flange, or at the level of step shapes.

The figure 8 represents a second step of the process for manufacturing the composite annular casing according to the invention.

The second step comprises the positioning of the main fibrous reinforcement 38, so that the latter covers the tubular surface 66 and the radial surface 68 of the mold 62, as well as the auxiliary reinforcement 56, and possible other auxiliary reinforcements. During this step, the main reinforcement 38 comes into contact with the core 58 of the auxiliary reinforcement 56 at a contact surface with a generally straight profile.

The figure 9 shows the main reinforcement 38 and the auxiliary reinforcement 56 when they are both in place in the mold 62.

These reinforcements can match over the majority, preferably over at least 80%, more preferably over the entire thickness of the flange 44 or 52 and / or over the majority, preferably over at least 80%, more preferably over the the entire thickness of the partition 42 of the main reinforcement 38. When they fit together, they compress each other, the large side of the triangle is curved, and the rounding (50, 54) at the junction between the flange and the partition 42 of the main reinforcement crashes, flattens. The reinforcements can match over the majority, preferably the entire radial height of the core of the auxiliary reinforcement.

At the interface 71 of the preforms, fibers of the two preforms can pass through said interface 71, be interposed at the same level. They can overlap which improves consistency in combination with the matrix.

The figure 10 represents a third step of the manufacturing process of the composite annular casing according to the invention.

The third step of the process comprises closing the injection mold, the latter comprising at least a second mold 72 or counter-mold 72 which is applied against the main reinforcement 38 and compacts it. The counter-mold 72 can be a maie mold. The counter-mold 72 can reduce the thickness of the partition and / or the thickness of the flange (44, 52) of the main reinforcement 38. The mold 62 and the counter-mold 72 define between them a mold cavity essentially reproducing the shape of the annular casing. During this step, the core 58 can be compacted again. The effect of closing the mold can make it possible to reduce the thicknesses of the preforms by at least 5%, preferably at least 20%.

The figure 11 represents a fourth step of the manufacturing process of the composite annular casing according to the invention.

The fourth step comprises the injection of a resin 74, in particular an organic resin, into the injection mold. The resin can be a thermoplastic resin such as epoxy, polyetherimide (PEI), polyetheretherketone (PEEK). The injection may consist in impregnating the preforms, according to a process of the RTM type (acronym for Resin Transfer Molding). The method may include injection of a filled resin. Optionally, the injection can be assisted by aspiration.

Following the injection, the mold can be maintained for a period of at least one hour at a temperature above 50 ° C, preferably above 120 ° C. Following these steps, the resin polymerizes and hardens and can adhere to the reinforcements; thus forming a solid body.

The figure 12 shows a fifth step in the process for manufacturing the composite annular casing 28 according to the invention.

The fifth step comprises demolding the composite annular casing 28. First, the backing mold is removed from the mold 62, then a demolding force is applied to the casing to extract it from the mold.

The casing 28 resulting from the molding can be machined. It can be perforated at the level of the flanges 30 to produce fixing holes, and / or at the level of the wall 34 to allow the blades to be fitted. Optionally, the axial and / or annular flanges can be cut to remove heterogeneous ends, specially added to improve the quality of the finished flanges.

Once polymerized, the matrix binds the main reinforcement 38 and the auxiliary reinforcement 56. It has a continuity of material at the interface 71 between the reinforcements (38; 56), which makes it possible to join them together. This configuration favors the anchoring of the reinforcements. The core of the auxiliary reinforcement 56 comprises fibers which extend radially, over at least 10%, preferably over at least the whole, more preferably over at least twice the thickness of the wall 34. These fibers improve the resistance in radial compression. edge and allow the edge to form a block. These fibers extend from the ridge 76 of the housing 28 to the main reinforcement 38.

The main fibrous reinforcement 38 extends continuously along the wall 38 and the flange 30 forming an angled and generally rounded portion at the ridge. The core 58 extends along the ridge 76 so as to fill the volume between the ridge and the bent portion of the main reinforcement 38. The interface 71 may have a generally curved and substantially flattened profile. The reinforcements (38 and 56) can be configured so that the casing 28 has continuity and homogeneity of fiber density in the junction 80 between the flange 30 and the wall 34 and / or along the surfaces of the junction. 80. This homogeneity improves the mechanical strength and endurance of the casing 28 which can be subjected to vibrations, chemical attack at a temperature above 170 ° C during operation of the turbomachine.

The general radius of the rounded interface and / or the thickness of the wall is / are greater than 1%, preferably greater than 2%, more preferably greater than 4%, possibly greater than 6% of the radius of the sharp edge.

The housing 28 has a sharp edge 76 forming a projecting angle. This ridge can be integrated into the turbomachine, without requiring additional machining. The ridge 76 can be generally perpendicular, which allows a smooth junction to be made when it is brought into line with a corresponding ridge. The meeting of the two edges makes it possible to produce a guiding surface of a flow without a projection which would interfere with the good flow of the flow. This meeting can also form an attachment zone without roughness, for example to come to support a blade platform therein with a view to its positioning and its attachment.

Claims (15)

1. Composite annular casing (28) of a turbomachine (2), in particular of a low-pressure compressor (4), including:

   - a wall (34) of generally circular form or in a circular arc;

   - a mounting flange (30) extending radially from one side of the wall (34), forming an edge (76) together with the said wall;

   - a main fibrous reinforcement (38) extending in a continuous manner along the wall and of the flange and forming an angled portion and rounded in the area of the edge, the main fibrous reinforcement (38) comprising a preform (40) made of a plurality of folds (46), each fold (46) comprising woven fibres, and

   - an auxiliary fibrous reinforcement (56) extending along the edge (76);

   - a matrix;

   the auxiliary reinforcement (56) comprising a core (58) extending along the edge (76) in such a way as to occupy the volume between the edge and the angled portion of the main reinforcement (38), the core of the auxiliary reinforcement (56) comprises fibres (60) which extend radially from the edge (76) as far as the main reinforcement (38), said fibres (60) being of the same nature than the woven fibres of the folds (46) of the main reinforcement.
2. Casing (28) according to claim 1, characterized in that the core (58) of the auxiliary reinforcement (56) comprises a braided or woven strand, optionally in a three-dimensional manner.
3. Casing (28) according to one of claims 1 and 2, characterized in that the transverse section of the core of the auxiliary reinforcement (56) presents a profile of generally triangular form, optionally of a right-angled triangle of which the right angle is arranged in the area of the sharp edge (76).
4. Casing (28) according to one of claims 1 to 3, characterized in that the main reinforcement (38) and the auxiliary reinforcement (56) are essentially in contact over the whole of the radial thickness of the wall (34) and/or over the whole of the axial thickness of the mounting flange (30).
5. Casing (28) according to one of claims 1 to 4, characterized in that the core of the auxiliary reinforcement (56) presents a homogeneous fibre density perpendicular to its prolongation.
6. Casing (28) according to one of claims 1 to 5, characterized in that the mounting flange is an annular mounting flange (30) and/or an axial mounting flange, the annular casing (28) preferably being an annular case-half extending over a semi-circle which comprises axial flanges arranged laterally on the cylindrical portion (34) and opposing annular flanges arranged at the axial extremities of the cylindrical portion (34).
7. Casing (28) according to one of claims 1 to 6, characterized in that the fibres (60) of the core (58) of the auxiliary reinforcement (56) extend mainly parallel to the edge (76), each portion of fibres (60) of the auxiliary reinforcement (56) preferably being inclined in relation to the edge at an angle of less than 40°, and more preferably of less than 20°.
8. Casing (28) according to one of claims 1 to 7, characterized in that the fibres (60) of the main reinforcement (38) and of the core of the auxiliary reinforcement (56) are of the same length and/or of the same diameter.
9. Casing (28) according to one of claims 1 to 8, characterized in that the fibres of the main reinforcement (38) and of the core of the auxiliary reinforcement (56) are intertwined at the interface (71) between the main reinforcement (38) and the auxiliary reinforcement (56), the fibres of the reinforcements preferably being arranged in bundles of fibres which are intertwined across the interface.
10. Casing (28) according to one of claims 1 to 9, characterized in that the main reinforcement (38) and the core of the auxiliary reinforcement (56) each have a homogeneous density of the fibres (60), the ratio of the densities of the fibres of the reinforcements preferably being between 0.5 and 1.50; preferably between 0.80 and 1.20; more preferably between 0.95 and 1.05.
11. Turbomachine (2) comprising a composite annular casing (28), characterized in that the composite annular casing (28) is in accordance with one of claims 1 to 10, the matrix preferably being an organic matrix on the basis of polyetherimide, epoxy, or polyether ether ketone; the main reinforcement (38) being a fibrous preform comprising a stack of fibrous folds (46) with carbon fibres and glass fibres, each fibrous fold comprising fibres (60) arranged in bundles of woven fibres in at least two directions.
12. Turbomachine (2) according to claim 11, characterized in that it comprises a intermediate blower casing (32), a low-pressure compressor (4) with annular rows of stationary blades (26) and a separation nose (22), the annular casing (28) comprising an annular mounting flange (30) at each axial extremity, including an upstream flange and an downstream flange, the annular casing (28) having a reduction in its radius in the downstream direction, the annular casing (28) preferably being an external principal structure of the compressor (4) to which the rows of blades (26) are fixed, the separation nose (22) via the upstream flange, the intermediate blower casing (32) via the downstream flange, the annular casing (28) further comprising an alternation of annular layers of abradable material (36) and annular surfaces for the mounting of the blades, the annular casing (28) being formed from half shells separated by an axially extending plane.
13. Method of manufacturing a composite annular casing (28) of a turbomachine (2) which comprises a wall (34) presenting a generally circular profile or in a circular arc, a mounting flange (30) extending radially from one side of the wall (34) and forming together with the wall an edge (76), the method comprising the following steps:

    (a) positioning (107) of an auxiliary reinforcement (56) in a corner (70) of a moulding surface (64) of an injection mould, said corner forming the edge (76);

    (b) positioning (108) of a main reinforcement (38) against the moulding surface (64) by adapting their form to that of the auxiliary reinforcement (56) in the area of the corner (70), the main fibrous reinforcement (38) comprising a preform (40) made of a plurality of folds (46), each fold (46) comprising woven fibres;

    (c) closing of the injection mould;

    (d) injection of a resin (74) and polymerization of the resin (74);

    (e) demoulding of the casing (28),

    method wherein the core of the auxiliary reinforcement (56) comprises fibres (60) which, after the step (b), extend radially from the edge (76) to the main reinforcement (38), said fibres (60) being of the same nature than the woven fibres of the folds (46) of the main reinforcement
14. Method according to Claim 13, characterized in that, before the step (b) of positioning (108) a main reinforcement (38), said reinforcement (38) is produced with a rounding (50; 54) intended to come into contact with a contact surface of the auxiliary reinforcement (56), preferably on completion of the step (b), the rounding of the main reinforcement being flattened and the contact surface of the auxiliary reinforcement being curved inwards.
15. Method according to one of claims 13 and 14, characterized in that, in the course of the step (c) of closing of the injection mould, the main reinforcement (38) is compacted and/or the main reinforcement (38) and the core (58) are compacted mutually.

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